FeVO 4 -II, a metastable phase so far produced under high (5), on the other hand, constructed the pressure-product pressures, has been synthesized by a hydrothermal method from diagram of the Fe 1Οͺx V x O 2 system for 0 Υ
x Υ
0.5 at 800ΠC a solution of VOCl 2 and FeCl 3 . FeVO 4 -II crystallizes in the where FeVO 4 (x Ο 0.5) exhibited successive transformaorthorhombic system: Cmcm, a β«Ψβ¬ 5.6284( ) A Λ, b β«Ψβ¬ 8.2724(7) tions I Η II Η III Η IV with increasing pressures. A Λ, c β«Ψβ¬ 6.1118(6) A Λ, with Z β«Ψβ¬ 4. The single-crystal structure In the present study, we have empoyed a hydrothermal refinements verified a CrVO 4 -type structure and converged to method and successfully obtained single crystals of the R/R w β«Ψβ¬ 0.035/0.029 for 324 reflections with I ΟΎ 3 (I). The metastable polymorph FeVO 4 -II. A single-crystal X-ray structure consists of FeO 6 octahedra and VO 4 tetrahedra where analysis has verified the CrVO 4 -type structure and the meaedge-sharing FeO 6 octahedra form isolated FeO 4 chains running surements of magnetic susceptibility and Mo Β¨ssbauer effect parallel to the c axis and the chains are joined by VO 4 tetrahedra. The temperature dependence of magnetic susceptibility revealed the occurrence of antiferromagnetic order. featured by a broad maximum around 52 K suggests the predominance of one-dimensional antiferromagnetic interactions EXPERIMENTAL in the FeO 4 chains. A three-dimensional antiferromagnetic order is attained somewhere below 40 K yielding a hyperfine field Sample Preparation of 483 KOe at 4.2 K observed in the Mo Β¨ssbauer spectrum. Β© 1996 Starting materials used in the hydrothermal synthesis Academic Press, Inc.
were aqueous solutions of VOCl 2 and FeCl 3 with V/Fe molar ratios of 0.5 to 1.0 where the concentration of FeCl 3 FeO 5 trigonal bipyramid, and three VO 4 tetrahedra where 0.99(1), which confirms the stoichiometric composition of Fe-O polyhedra form a doubly bent chain (2). Other poly-FeVO 4 . As shown in an SEM micrograph in Fig. , the morphs were assumed from the powder X-ray diffraction products were single-crystalline granules with a particle data to have the orthorhombic CrVO 4 structure for size of 0.1 to 0.3 mm. FeVO 4 -II, the orthorhombic Ν°-PbO 2 for FeVO 4 -III, and the monoclinic wolframite NiWO 4 for FeVO 4 -IV (1,3,4); Magnetic Property Measurements however, no structures of the phases have been fully char-Magnetic susceptibility was measured by using a SQUID acterized. The metastable phases of FeVO 4 are normally magnetometer under a magnetic field of 1000 G in a temformed under high-pressure and high-temperature condiperature range from 5 to 300 K. The Mo Β¨ssbauer effect was tions. Muller and Joubert (1) reported that FeVO 4 -III and observed at 4.2 K, 77 K, and RT using 57 Co/Rh as a Ν²-ray IV were obtained directly by the high-pressure and highsource and pure Fe metal as a standard. As-synthesized temperature synthesis and FeVO 4 -II emerged as an intermediate phase transformed from FeVO 4 -III around 540ΠC granules were used in both measurements.